Sweetheart - Picked up on a sad Batty fast and knows love and affection are the cure 99% of the time. He's often starving for touch if he's having a bad time so cuddling is his fav comfort activity
Dear - A grouchy Redhot is a bit tricky to pick up on sometimes but a tell tale is him turning down a brawling match. He struggles with the mushy stuff but he'll still try and often, baking some sweets helps makes Redhot feel better. They don't even have to be good, it's just the process and participating in it with his partner that calms him down
Sourpuss - Baby notices a sad kittycat immediately because they are often the most happiest of the four. She is a wee bit awkward with her approach but knows they enjoy sitting in her lap and binging shows with her while snacking on candy so she pulls up her fav anime streaming service, pulls them in, and gives them some sour gummy worms.
Honey - She can pick up on a sad Halite quickly because he's pretty transparent and will often tell her if he's having a hard time. His music and singing also gets sadder. She tends to just sit him down and have them talk it out. And if that's too much for him, she'll just pop on a playlist of his fav songs (she kept track and adds more and more to the list whenever he seems to find a human song he really enjoys) and lets it play as they just lay in bed together.